EP1847999B1 - Schaltung und Verfahren zur Bestimmung des resistiven Status einer resistiven Speicherzelle - Google Patents

Schaltung und Verfahren zur Bestimmung des resistiven Status einer resistiven Speicherzelle Download PDF

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Publication number
EP1847999B1
EP1847999B1 EP07105990A EP07105990A EP1847999B1 EP 1847999 B1 EP1847999 B1 EP 1847999B1 EP 07105990 A EP07105990 A EP 07105990A EP 07105990 A EP07105990 A EP 07105990A EP 1847999 B1 EP1847999 B1 EP 1847999B1
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EP
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Prior art keywords
memory cell
current
resistive
read
read circuit
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EP07105990A
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English (en)
French (fr)
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EP1847999A3 (de
EP1847999A2 (de
EP1847999A9 (de
Inventor
Jens Egerer
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Qimonda AG
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Qimonda AG
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
    • G11C13/0009—RRAM elements whose operation depends upon chemical change
    • G11C13/0011—RRAM elements whose operation depends upon chemical change comprising conductive bridging RAM [CBRAM] or programming metallization cells [PMCs]
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/56—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency
    • G11C11/5614—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency using conductive bridging RAM [CBRAM] or programming metallization cells [PMC]
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/56—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency
    • G11C11/5678—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency using amorphous/crystalline phase transition storage elements
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
    • G11C13/0004—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements comprising amorphous/crystalline phase transition cells
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
    • G11C13/0021—Auxiliary circuits
    • G11C13/004—Reading or sensing circuits or methods
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
    • G11C13/0021—Auxiliary circuits
    • G11C13/004—Reading or sensing circuits or methods
    • G11C2013/0054—Read is performed on a reference element, e.g. cell, and the reference sensed value is used to compare the sensed value of the selected cell

Definitions

  • the invention relates to a circuit and a method of determining the resistive state of a resistive memory cell.
  • a reference memory cell is used to provide the reference voltage since it will be subjected to the same temperature and voltage influences as the cell being read and it will typically be affected by manufacturing tolerances in a manner similar to the cell being read.
  • a resistive memory cell has a resistance that can be programmed to have either a high resistance value or a low resistance value when accessed.
  • a conventional resistive memory cell is a PMC (programmable metallization cell), which utilizes electrochemical control of nanoscale quantities of a metal in thin films of solid electrolyte.
  • a PMC can have a low resistance value of, for example, 10 4 ohms and a high resistance value of, for example, 10 9 ohms.
  • the low resistance value can represent a data bit having a logic 1 value and the high resistance value can represent a data bit having a logic 0 value (or vice-versa).
  • phase change memory cell which has a high resistance value in an amorphous state and a low resistance vale in a crystalline state.
  • a heater element is used to heat a programmable volume of the phase change memory cell and to place the programmable volume into the amorphous state or the crystalline state.
  • US 6,597,598 discloses an arrangement to read a memory cell using the bit, bit bar method in which each memory cell is measured against a corresponding reference cell which carries the complementary bit value to the value carried by the cell whose value is to be read.
  • US 2004/0095825 discloses an arrangement to read a memory cell using the bit, bit bar method in which each memory cell is measured against a corresponding reference cell which carries the complementary bit value to the value carried by the cell whose value is to be read.
  • a reference current is supplied by an external reference current generator.
  • US 6,621,729 discloses an arrangement to read a memory cell by comparing a value of current equal to twice the current generated across the memory cell with a reference current produced by adding the currents generated across two reference memory cells, one reference memory cell having a high resistance value and the other reference memory cell having a low resistance value.
  • the arrangement comprises a differential amplifier arrangement, an equalizer and a further current source.
  • US 6,501,697 discloses an arrangement to read a memory cell by comparing a value of current from the memory cell with a reference current produced by averaging the current from two reference cells by summing their currents and halving the addition.
  • One reference cell has a high resistance value, the other has a low resistance value.
  • a method and a circuit as described in the claims are disclosed for determining the resistive state of a resistive memory cell being read.
  • the method and operation of the circuit are based on determining the resistive state of the memory cell by comparing a current dependent on the resistive state of the memory cell with a reference current.
  • Fig. 1 is a basic block diagram of a circuit for determining the resistive state of a resistive memory cell
  • Fig. 2 is a schematic diagram of a circuit implementing a first embodiment of a read circuit
  • Fig. 3 is a schematic diagram of a circuit implementing a second embodiment of a read circuit
  • Fig. 4 is a schematic diagram of a circuit implementing a third embodiment of a read circuit.
  • Fig. 5 is a schematic diagram of a circuit implementing a read circuit.
  • PMCs programmable metallization cells
  • resistive memory cells that can be used when implementing the invention.
  • the invention should not be construed as being limited to being used with PMCs.
  • Phase change memory cells for example, as well as other types of memory cells having a programmable resistance could also be used.
  • the voltage across the resistance of the memory cell is typically held in the range from 100mV to 200mV.
  • a typical current flowing through the memory resistance will be 10uA.
  • the PMC has a high resistance state with a high resistance value of, for example 10 9 ohms
  • a typical current flowing through the memory resistance will be 100pA.
  • the low resistance state is assigned to represent a data bit having a logic 1 value and the high resistance state is assigned to represent a data bit having a logic 0 value, although the opposite assignment could alternatively be made.
  • the invention is based on reading the content of a resistive memory cell by comparing the current flowing through the resistive memory cell being read with a reference current that is, e.g., dependent on the current flowing through one or more reference resistive memory cells.
  • Fig. 1 is a basic block diagram of a circuit 100 for determining the resistive state of the resistive memory cell 105.
  • the stored data bit is a logic 1 or logic 0, depending on the resistive state of the resistance 106 of the memory cell 105. For example, if it is determined that the resistance 106 is in the low resistive state, the resistive memory cell 105 is storing a logic 1.
  • Comparing means in this example a read circuit 145, is provided for comparing the current in branch D with the current in branch E in order to determine the resistive state of the memory cell 105 and thus, the data bit stored therein.
  • the current in branch D is dependent on the current I cell flowing through the memory cell 105 and is thus dependent on the value of the resistance 106 of the memory cell 105.
  • the current in branch E is a reference current I ref .
  • One or more reference resistive memory cells 110, 115 serve as a means for providing a reference current I ref .
  • the reference resistive memory cells 110, 11 5 will be subjected to the same temperature, voltage, and current influences as the memory cell 105 being read and will typically be affected by manufacturing tolerances in a manner similar to the memory cell 105 being read.
  • the reference current I ref may be dependent on the current flowing through the resistance of only one reference resistive memory cell.
  • the reference current I ref may be dependent on the current I 1 flowing through the resistance 111 of the reference resistive memory cell 110.
  • the reference resistive memory cell 110 is, for example, set to have a low resistance value.
  • the reference current I ref is obtained by using two reference resistive memory cells 110, 115.
  • the reference current I ref will then be dependent on the current I 1 flowing through the reference resistive memory cell 110 and will also be dependent on the current I 2 flowing through the reference resistive memory cell 115.
  • the reference resistive memory cell 115 is set to have the high resistance state, which in this example, has been assigned the logic value 0.
  • the reference current I ref is, for example, simply equal to the sum of the currents flowing through both reference resistive memory cells 110 and 115, however, this sum could be multiplied by a suitable factor in some cases. In fact, the current flowing through either one or both of the reference resistive memory cells 110, 115 could be multiplied by a suitable factor.
  • the important aspect is simply to obtain a reference current I ref that can be compared with a current dependent on the current I cell flowing through the memory cell 105 so that the resistive state of the memory cell 105 and thus the data bit being stored in the memory cell 105 can be reliably determined.
  • the read circuit 145 provides an output signal, out_n, depending on the relationship between the magnitude of the current in branch D and the magnitude of the current in branch E, which is the reference current I ref . If read circuit 145 finds that the current in branch D is higher than the reference current I ref , then the output signal out_n indicates that the memory cell 105 has a low resistance state and is storing a data bit having a logic 1 value. If, however, the read circuit 145 finds that the current in branch D is lower than the reference current I ref , then the output signal out_n indicates that the memory cell 105 has a high resistance state and is storing a data bit having a logic 0 value.
  • the read circuit 145 basically functions as a current comparator and one of ordinary skill in the art should now be enabled to construct the read circuit 145 in a number of different ways. Four particular examples of constructing the read circuit 145 will be provided later on in this text. The invention, however, should not be construed as being limited to these examples.
  • a current mirror 155 may be used to mirror the current I cell flowing through the resistance 106 of the memory cell 105 into branch D of the read circuit 145. Thus, the current mirror 155 serves as a means for feeding the current I cell to the read circuit 145.
  • a current mirror 135 is used to mirror the current I 1 flowing through the resistance 111 of the reference resistive memory cell 110 into another branch E of the read circuit 145. Thus, the current mirror 135 serves as a means for feeding the current I 1 to the read circuit 145.
  • a current mirror 140 is provided to mirror the current I 2 flowing through the resistance 116 of the second reference resistive memory cell 115 into the branch E of the read circuit 145 so that the reference current I ref in branch E will be the sum of the currents from current mirror 135 and current mirror 140.
  • the current mirror 140 will then serve as a means for feeding the current I 2 to the read circuit 145.
  • the mirror ratios of current mirror 155, current mirror 135, and current mirror 140 should be chosen to cooperate in a way enabling the read circuit 145 to clearly make a determination as to whether the current in branch D or the reference current I ref in branch E is greater. In this manner the data bit being stored in the memory cell 105 can clearly be determined.
  • level shifters may need to be provided.
  • the voltage across the resistance of a PMC will typically need to be limited to be in the range from 100mV to 200n2V.
  • Level shifting means specifically, the level shifters 120, 125, and 130 have been provided for this purpose. By shifting the voltage between each resistive memory cell 105, 110, and 115 and the respective current mirror 155, 135, and 140, the voltage across the resistance 106, 111, and 116 of each resistive memory cell 105, 110, and 115 can be limited to the desired value.
  • the level shifters 120, 125, and 130 can be designed to include select transistors to access the resistive memory cells 105, 110, and 115.
  • a level shifter design including select transistors can be similar to the conventional design used in a DRAM (Dynamic Random Access Memory). The gate of a select transistor can be connected to a wordline and the drain of the select transistor can be connected to the bitline.
  • constant currents could be added to flow through the current mirrors 135, 155 in the branches B and C to ground and in one option also through the current mirror 140 in branch A to ground in order to increase the currents in the current mirrors (135, 155 and possibly 140) and in the read circuit 145. Theoretically this would speed up the evaluation in the read circuit 145.
  • constant additional currents could also be added at other locations, for example, directly into the branches D and E of the read circuit 145.
  • An inverter 160 can be provided to drive a higher capacitive load. In some cases where necessary because of a particular implementation of the read circuit 145, the inverter 160 can pull the output (out) to the full logic levels of the chip.
  • a memory chip can include a number of read circuits 145A, 145B, 145C, or 145D sufficient to enable a large number of cells to be read in parallel and to enable the amplified signals to be switched onto a data bus. Similar to the read amplifiers configured in a conventional DRAM, for example, one read circuit 145A, 14SF3, 145C, or 145D can be provided in the layout for every four bitlines.
  • Each of the read circuits 145A, 145B, 145C, and 145D use a relatively small area on the chip when compared to that required for implementing conventional operational amplifiers.
  • the read circuits 145A, 145B, 145C, and 145D can be implemented quite simply and large transistors are not required for reducing voltage offset errors as is required when using a conventional operational amplifier, for example, to read a data bit from a resistive memory cell.
  • the full logic level of the chip or very close to that level is obtained at the output of each read circuit 145A, 145B, 145C, and 145D and an additional level shifter is not required for this purpose.
  • Fig. 2 is a schematic diagram of a circuit 100A for determining the resistive state of the resistive memory cell 105.
  • the circuit 100A implements a first exemplary embodiment of a read circuit 145A for reading the resistive memory cell 105.
  • the read circuit 145A is constructed as a current mirror using NFETs N32 and N33 and is indicated using dashed lines.
  • the current I 1 flowing through the reference cell 110 is mirrored into branch E of the read circuit 145A by the current mirror formed by PFETs P21 and P22.
  • the current I 2 flowing through the reference cell 115 is additively mirrored into branch E of the read circuit 145A by the current mirror formed by PFETs P11 and P12.
  • the current I cell flowing through the resistive memory cell 105 is mirrored into branch D of the read circuit 145A by the current mirror formed by PFETs P31 and P32.
  • the current mirror formed by PFETs P31 and P32 has a mirror ratio of 1:1.
  • the read circuit 145A then mirrors the current I cell from branch D into the output branch E using a mirror ratio of 1:2.
  • the PFETs P32 and P22 work against the NFETs N32 and N33 of the read circuit 145A so that node Z of the read circuit 145A will be pulled to the voltage assigned to logic 0 or logic 1 depending on whether twice the current I cell flowing through the resistive memory cell 105 is larger than the sum of the currents I 1 and I 2 flowing through the reference cells 110 and 115, respectively.
  • the mirror consisting of P31 and P32 and the mirror formed by N32 and N33 for example cooperate to provide at least 1.5 times, for example 2 times, the amplification factor provided by the current mirror P21 and P22 (and possibly 2 times that of P11 and P12 as well).
  • the maximum current flowing through branch E is determined by the smaller current provided to the read circuit 145A.
  • the current mirrored to N33 from N32 which is 20uA when a PMC is used, is limited by the reference current of 10uA.
  • the current mirrored to N33 from N32 which is approximately 200pA when a PMC is used, limits the current flowing through branch E to approximately 200pA.
  • the inverter 160 may be provided to drive a higher capacitive load and can pull the output (out) to the full logic levels of the chip, while providing minimal leakage current. It may be advantageous to speed up the switching time by precharging node Z to a potential lying in the middle between those assigned to logic 0 and logic 1, however in this case switches may be required as a measure against high leakage currents.
  • One or more non-illustrated switching transistors can be used to switch the current mirror formed by N32 and N33 on and off.
  • Fig. 3 is a schematic diagram of a circuit 100B for determining the resistive state of the resistive memory cell 105.
  • the circuit 100B implements a second exemplary embodiment of a read circuit 145B for reading the resistive memory cell 105.
  • the read circuit 145B includes NFETs N31 and N22 that are cross-coupled similar to the way that such transistors are connected in level shifters.
  • the mirror ratio of the current mirror formed by P31 and P32 has been set to 1:2. Other mirror ratios could be used, for example, 1:1.5. Alternatively, the mirror ratios of all the current mirrors could be adjusted to suitable values just as long as the read circuit 145B can distinguish the current mirrored into branch D from the reference current in branch E.
  • One or more non-illustrated transistors may be provided for switching on the read circuit 145B for reading the memory cell 105. It may also be advantageous to precharge the nodes Y and Z to the logic 0 voltage, the logic 1 voltage, or to a level between the logic 0 and logic 1 voltages to speed up the switching time of the circuit 145B. In this case, however, it may be necessary to provide switches to protect against high leakage currents when the circuit 100B is switched off. In addition, leakage currents could be prevented by using one or more suitable transistors to switch off NFETs N31 and N22.
  • Fig. 4 is a schematic diagram of a circuit 100C for determining the resistive state of the resistive memory cell 105.
  • the circuit 100C implements a third exemplary embodiment of a read circuit 145C for reading the resistive memory cell 105.
  • the read circuit 245C is based on a sense amplifier - clocked latch - that is used in a DRAM (dynamic random access memory). The full voltage level of the memory chip is obtained at node Z and, therefore, level shifters need not be provided for this purpose.
  • the cross-coupling of the inverters, formed by P33, N34 and P23, N23, enable high amplification and speed.
  • the read circuit 145C enables small transistors to be used when compared to implementations using operation amplifiers since large transistors are not required for reducing voltage offset errors.
  • the current mirror formed by PFET P31 and PFET P32 mirrors the current I cell flowing through the resistive memory cell 105 into branch D of the read circuit 145C.
  • This current mirror for example has a mirror ratio acting to increase the mirrored current into branch D.
  • the mirror ratio has been set to 1:2.
  • the mirror ratio may be higher, for example 1:3, or lower, for example 1:1.5, just as long as it enables the read circuit 145C to distinguish between the mirrored current from the resistive memory cell 105 and the mirrored current from the reference cell 110 or cells 110 and 115.
  • the read circuit 145C it is also possible to enable the read circuit 145C to distinguish between the mirrored currents by setting the mirror ratio of the current mirror formed by P21 and P22 and possibly also the current mirror formed by P11 and P12 to decrease the value of the mirrored current or currents with respect to the current flowing through the reference cells.
  • the reference resistive memory cell 110 stores a logic 1, which corresponds to a resistance value of about 10 4 ohms when PMCs are being read. The current through the reference resistive memory cell 110 will then lie in the range of approximately 10uA.
  • the level shifters 120, 125, and 130 can be designed to include select transistors to access the memory cells 105, 110, and 115 in a manner similar to the design used in a DRAM.
  • the gate of a select transistor can be connected to a wordline and the drain of the select transistor can be connected to the bitline.
  • node Z of the read circuit 145C When one reference cell 110 is used to provide a reference current, node Z of the read circuit 145C will be pulled to the voltage assigned to logic 0 or logic 1 depending on whether twice the current I cell flowing through the resistive memory cell 105 is larger than the current I 1 flowing through the reference cell 110. When two reference cells 110, 115 are used, node Z of the read circuit 145C will be pulled to the voltage assigned to logic 0 or logic 1 depending on whether twice the current I cell flowing through the resistive memory cell 105 is larger than the sum of the current I 1 flowing through the reference cell 110 and the current I 2 flowing through the reference cell 115.
  • Transistor P99 and the input signal en_n are used to switch the read circuit 145C on and off.
  • transistors N98 and N99 can be used to place each of the nodes Y and Z at a defined voltage value so that when the read circuit 145C is switched on, the read circuit 145C starts from the defined voltage value.
  • the defined voltage value can be, for example, zero volts or a voltage halfway between the voltages assigned to logic 0 and logic 1.
  • the signal EQ and the NFET N35 can be used to equalize nodes Y and Z.
  • the output signal out_n at node Z is pulled to the voltage assigned to logic 0 or logic 1 depending on whether twice the current I cell of the resistive memory cell 105 is smaller or larger than the reference current I ref , which is obtained from reference memory cell 110 or reference memory cells 110 and 115.
  • An inverter 160 can be provided at node Z to further amplify the output signal. This inverter 160 can drive a higher capacitive load.
  • Fig. 5 is a schematic diagram of a circuit 100D for determining the resistive state of the resistive memory cell 105.
  • the read circuit 145D is constructed similarly to the read circuit 145C, but additionally has a subtraction circuit formed by N122 and N123 and a subtraction circuit formed by N133 and N132. Only one reference resistive memory cell 110 has been used in this example.
  • the current mirror formed by PFETs P21 and P22b mirrors the current I 1 flowing through the reference resistive memory cell 110 into branch G of the read circuit 145D.
  • the current mirror formed by PFETs P21 and P22a mirrors the current I 1 flowing through the reference resistive memory cell 110 into branch F of the read circuit 145D.
  • the current mirror formed by PFETs P31 and P32b has a mirror ratio of 1:2 and mirrors the current I cell flowing through the resistive memory cell 105 being read into branch D.
  • the current mirror formed by PFETs P31 and P32a has a mirror ratio of 1:2 and mirrors the current I cell flowing through the resistive memory cell 105 being read into branch E.
  • a subtraction circuit is formed by NFETs N122 and N123, which mirror the current I 1 into branch E where the current I 1 is subtracted from the current I cell .
  • Another subtraction circuit is formed by NFETs N132 and N133, which mirror the current I cell into branch F where the current I cell is subtracted from the current I 1 .
  • This cross-coupling causes the voltage difference between the nodes Y and Z of the read circuit 145D to become larger.
  • One of the nodes Y, Z will be pulled close to the positive supply voltage, while the other one of the nodes Y, Z will be pulled close to ground. If 2*I cell > I 1 , branch E (node Y) will be pulled up close to the positive supply voltage and branch F (node Z) will be pulled close to ground. If I 1 > 2*I cell , branch F will be pulled up close to the positive supply voltage and branch E will be pulled close to ground.
  • One advantage of this embodiment of the read circuit 145D is that the node pulled to ground is pulled down not only by the read circuit 145D, but also by the subtraction circuit formed by N122, N123 or N133, N132, even when the read circuit 145D is not yet switched on.
  • Transistor P99 and the input signal en_n are used to switch the read circuit 145D on and off.
  • transistors N98 and N99 can be used to place each of the nodes Y and Z at a defined voltage value so that when the read circuit 145D is switched on, the read circuit 145D starts from the defined voltage value.
  • the defined voltage value can be, for example, zero volts or a voltage halfway between logic 0 and logic 1.
  • the signal EQ and the NFET N35 can be used to equalize nodes Y and Z.
  • An inverter 160 can be provided at node Z to drive a higher capacitive load.

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  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Read Only Memory (AREA)
  • Semiconductor Memories (AREA)

Claims (12)

  1. Ein Verfahren zum Bestimmen eines resistiven Zustandes einer resistiven Speicherzelle (105), das Verfahren aufweisend:
    Bestimmen eines resistiven Zustandes einer gelesenen Speicherzelle (105) durch Vergleichen eines von dem resistiven Zustand der gelesenen Speicherzelle (105) abhängigen Stromes mit einem Referenzstrom, wobei der resistive Zustand der gelesenen Speicherzelle (105) ein durch die gelesene Speicherzelle gespeichertes Datenbit angibt,
    wobei das Verfahren aufweist:
    Verwenden eines ersten Stromspiegels (155) zum Zuführen des von dem resistiven Zustand der gelesenen Speicherzelle (105) abhängigen Stromes an einen Leseschaltkreis (145);
    Verwenden eines zweiten Stromspiegels (135) zum Zuführen eines ersten Referenzstromes, welcher von einem ersten resistiven Zustand einer auf einen tiefen Resistivitätswert gesetzten ersten resistiven Referenzspeicherzelle (110) abhängig ist, an einen Knoten (Z) in dem Leseschaltkreis (145);
    Verwenden eines dritten Stromspiegels (140) zum Zuführen eines zweiten Referenzstromes, welcher von einem zweiten resistiven Zustand einer auf einen hohen Resistivitätswert gesetzten zweiten resistiven Referenzspeicherzelle (115) abhängig ist, an den Knoten (Z) in dem Leseschaltkreis (145),
    sodass der erste Referenzstrom und der zweite Referenzstrom an dem Knoten addiert werden unter Verwendung des Leseschaltkreises (145) zum Ausführen des Additionsschrittes,
    wobei die Spiegelverhältnisse des ersten Stromspiegels (155), des zweiten Stromspiegels (135) und des dritten Stromspiegels (140) derart zusammenwirken, dass der Leseschaltkreis (145) in der Lage ist, ein Signal am Knoten (Z) zu erzeugen, aus dem bestimmt werden kann, ob der vom resistiven Zustand der Speicherzelle (105) abhängige Strom oder der Referenzstrom größer ist.
  2. Verfahren gemäß Anspruch 1, wobei die gelesene Speicherzelle (105) und die Referenzspeicherzellen (110, 115) aus einer Gruppe ausgewählt werden, die aus programmierbaren Metallisationszellen und Phasenänderungsspeicherzellen besteht.
  3. Verfahren gemäß Anspruch 1, wobei der erste Stromspiegel (155) ein anderes Stromspiegelverhältnis hat als der zweite Stromspiegel (135).
  4. Verfahren gemäß Anspruch 1, wobei der Leseschaltkreis (145) einen Stromspiegel aufweist, welcher einen ersten Ast, dem der von dem resistiven Zustand der gelesenen Speicherzelle (105) abhängige Strom zugeführt wird, und einen zweiten Ast aufweist, dem der Referenzstrom zugeführt wird.
  5. Verfahren gemäß Anspruch 1, wobei der Leseschaltkreis eine Mehrzahl von überkreuz verschalteten Feldeffekttransistoren aufweist.
  6. Verfahren gemäß Anspruch 1, ferner aufweisend:
    Verwenden eines ersten Pegelschiebers (120) zum Verschieben einer zwischen der gelesenen Speicherzelle (105) und dem ersten Stromspiegel (155) anliegenden Spannung;
    Verwenden eines zweiten Pegelschiebers (125) zum Verschieben einer zwischen der Referenzspeicherzelle (110) und dem zweiten Stromspiegel (135) anliegenden Spannung.
  7. Ein Speicherschaltkreis, aufweisend:
    eine resistive Speicherzelle (105);
    eine erste (110) und eine zweite (115) resistive Referenzspeicherzelle; und
    einen Leseschaltkreis (145), welcher einen ersten Eingang, welcher an die resistive Speicherzelle (105) gekoppelt ist, und einen zweiten Eingang aufweist, welcher an die erste und die zweite resistive Referenzspeicherzelle (110, 115) gekoppelt ist, wobei der Leseschaltkreis ferner einen Knoten (Z) aufweist, welcher an einen Ausgang gekoppelt ist zum Bereitstellen eines Ausgangssignals auf Basis eines Verhältnisses zwischen einem Referenzstrom von der ersten und der zweiten resistiven Referenzspeicherzelle (110, 115) und einem Strom, welcher von einem resistiven Zustand der Speicherzelle (105) abhängt, wobei
    ein erster Stromspiegel (155) bereitgestellt ist zum Zuführen des von dem resistiven Zustand der gelesenen Speicherzelle (105) abhängigen Stromes an den Leseschaltkreis (145);
    ein zweiter Stromspiegel (135) bereitgestellt ist zum Zuführen eines ersten Referenzstromes, welcher von einem ersten resistiven Zustand einer auf einen tiefen Resistivitätswert gesetzten ersten resistiven Referenzspeicherzelle (110) abhängig ist, an den Knoten (Z) in dem Leseschaltkreis (145);
    ein dritter Stromspiegel (140) bereitgestellt ist zum Zuführen eines zweiten Referenzstromes, welcher von einem zweiten resistiven Zustand einer auf einen hohen Resistivitätswert gesetzten zweiten resistiven Referenzspeicherzelle (115) abhängig ist, an den Knoten (Z) in dem Leseschaltkreis (145), sodass der erste Referenzstrom und der zweite Referenzstrom an dem Knoten (Z) addiert werden,
    wobei die Spiegelverhältnisse des ersten Stromspiegels (155), des zweiten Stromspiegels (135) und des dritten Stromspiegels (140) derart zusammenwirken, dass der Leseschaltkreis (145) in der Lage ist, das Ausgangssignal am Knoten (Z) zu erzeugen, aus dem bestimmt werden kann, ob der vom resistiven Zustand der Speicherzelle (105) abhängige Strom oder der Referenzstrom größer ist.
  8. Schaltkreis gemäß Anspruch 7, wobei
    der erste Stromspiegel (155) zwischen der resistiven Speicherzelle (105) und dem ersten Eingang des Leseschaltkreises (145) gekoppelt ist;
    der zweite Stromspiegel (135) zwischen der ersten resistiven Referenzspeicherzelle (110) und dem zweiten Eingang des Leseschaltkreises (145) gekoppelt ist.
  9. Schaltkreis gemäß Anspruch 8, ferner aufweisend:
    einen ersten Pegelschieber (120), welcher zwischen der resistiven Speicherzelle (105) und dem ersten Eingang des Leseschaltkreises (145) gekoppelt ist, und
    einen zweiten Pegelschieber (125), welcher zwischen der ersten resistiven Referenzspeicherzelle (110) und dem zweiten Eingang des Leseschaltkreises (145) gekoppelt ist.
  10. Schaltkreis gemäß Anspruch 7, wobei der Leseschaltkreis (145) einen Stromspiegel aufweist, welcher das Ausgangssignal bereitstellt, wobei der Stromspiegel einen ersten Ast, dem der von dem resistiven Zustand der resistiven Speicherzelle (105) abhängige Strom zugeführt wird, und einen zweiten Ast aufweist, dem der Referenzstrom zugeführt wird.
  11. Schaltkreis gemäß Anspruch 7, wobei der Leseschaltkreis eine Mehrzahl von überkreuz verschalteten Feldeffekttransistoren aufweist.
  12. Schaltkreis gemäß Anspruch 7, wobei die resistive Speicherzelle eine programmierbare Metallisationszelle oder eine Phasenänderungsspeicherzelle aufweist und wobei die mindestens eine erste und zweite resistive Referenzspeicherzelle eine programmierbare Metallisationszelle oder eine Phasenänderungsspeicherzelle aufweist.
EP07105990A 2006-04-19 2007-04-11 Schaltung und Verfahren zur Bestimmung des resistiven Status einer resistiven Speicherzelle Not-in-force EP1847999B1 (de)

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KR20070103691A (ko) 2007-10-24
CN101060012A (zh) 2007-10-24
JP2007294092A (ja) 2007-11-08
US20070247892A1 (en) 2007-10-25
EP1847999A2 (de) 2007-10-24
US7495971B2 (en) 2009-02-24
EP1847999A9 (de) 2011-06-15
JP2011096364A (ja) 2011-05-12
KR100876740B1 (ko) 2009-01-09
DE102006028107A1 (de) 2007-10-25

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